Active pixel sensors (APS) have become increasingly important for several applications, including large-area flat panel sensing arrays for imaging applications. Charge-to-voltage gain is important to increase the dynamic range and resolution of APS imagers. However, signal amplification is performed before the signal is carried to external amplifiers and analog to digital (A/D) converters, where the signal is then subject to noise from parasitic impedance.
FIG. 1 presents a schematic of prior art single stage APS circuit 1000, comprising output amplifier stage 1200 to amplify signal 1290 sent, via transistors 1210 and 1220, to external amplifier 1900. Signal 1290 is affected when a photoimpact at photosensor 1280 induces a current within photosensor 1280, thereby affecting the gate voltage of transistor 1210, which in turn affects signal 1290. Thus, APS circuit 1000 can be used to detect when such photoimpact has occurred at photosensor 1820. In some examples, photosensor 1280 can be configured to react to certain kinds of photoimpacts, whether it be from photons, X-rays, neutrons, and/or other particles and/or waves. As a result, APSs circuits can be used in different applications and fields, such as in medical fluoroscopy and for countermeasures to detect radiological weapons.
Current designs using metal-oxide-semiconductor (MOS) transistors, however, suffer from the effects of noise, which, among other drawbacks, limits the dynamic operation range of the APS. Therefore, a need exists in the art to develop APS devices and related methods that address such limitations described above to provide circuits with lower input-referred noise, higher gain, greater bandwidth, and faster sampling refresh rates than conventional APSs.
For simplicity and clarity of illustration, the drawing figures herein illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include,” and “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, device, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, system, article, device, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements or signals, electrically, mechanically or otherwise. Two or more electrical elements may be electrically coupled, but not mechanically or otherwise coupled; two or more mechanical elements may be mechanically coupled, but not electrically or otherwise coupled; two or more electrical elements may be mechanically coupled, but not electrically or otherwise coupled. Coupling (whether mechanical, electrical, or otherwise) may be for any length of time, e.g., permanent or semi-permanent or only for an instant.
“Electrical coupling” and the like should be broadly understood and include coupling involving any electrical signal, whether a power signal, a data signal, and/or other types or combinations of electrical signals. “Mechanical coupling” and the like should be broadly understood and include mechanical coupling of all types. The absence of the word “removably,” “removable,” and the like near the word “coupled,” and the like does not mean that the coupling, etc. in question is or is not removable.